By Katy Lam of My China Doll.
Adding tulle tutu skirts to the ultimate swimmers pattern is super fun and totally cute! Using a panel with a tutu skirt also makes for an awesome combination! I like to use poly stretch net such as the one available on the BOO! website.
With the method I am demonstrating, the top of the bottom layer is enclosed in the seam and the top layer is sewn on top.
Cut out your ultimate suit pattern pieces in your required size. Then take the front and back swimsuit pieces and measure down 5/8" (approximately 1.5cm) from the cut line for the skirt and draw a line. This is the placement for the bottom layer.
Cut along that line to create a top and bottom of front and back pattern pieces. Remember to add seam allowance to these cut edges. 
Cut your spandex and set aside.
For the tutu suit pictured above, I did 2 tiers and used 1 layer of magical white stretch net and 1 layer of white stretch net for each tier. 
To create the stretch net tiers, I have used the pattern piece for the gathered skirt from the ultimate suit (to utilise left over tulle after cutting the skirt for a dress). I increased the length of my pattern piece by 6 Inches (approximately 15.5cm) to its length to add more volume to the skirt. Cut 2 on the fold in the magical white stretch net and 2 in the white stretch net.
Alternatively, download the free Tulle Overlay pattern piece to create a circle based gathered skirt for your swimmers.
Align short edges and sew a seam to create a circle for each of your skirt pieces and mark the quarter points. I have sewn my seam on the sewing machine and then trimmed the seam allowance.
Take 1 magical white and 1 white stretch net skirt and layer them with the wrong side of the magical white on top of the right side of the white stretch net. Gather the 2 layers together. I like to use a zig zag gathering method because it allows for some stretch.
If you gather using a straight stitch, you will need to remove your stitches after attaching to ensure stretch is not restricted. 
Sew the top and bottom sections of the ultimate suit pieces but keep them as 2 separates. 
Take the sewn bottom half and turn it right side out. Mark quarter points. Align quarter points of skirt and swimsuit and baste it together using a straight stitch on the longest stitch length.
Attach top half of the ultimate suit over the tulle layers and bottoms using a triple stretch stitch followed by overlocking for durability. You can top stitch the tutu down if your prefer. 
Now you need to take the top half of the pattern for the front and back of your ultimate and cut along the pattern line used for skirt attachment. You will now have a thin piece that you can use to draw a guideline onto your swimsuit. 
Use fabric pen to draw a line on the front and back of your swimsuit. 
Placing wrong side of magical white on top of the right side of the white stretch net, gather the 2 layers together. I use a 1/4" (0.6cm) seam allowance from the top edge of the stretch net when I sewed my gathering stitch. It is important to keep this as precise as possible for the neatest finish. 
Match quarter points and attach the stretch net to the ultimate suit along marked guideline. Sew using a triple stretch stitch on top of the gathering stitch. The result is an exposed ruffle. 
Finish adding the elastic to the swimsuit as per pattern instructions. Be careful not to accidentally catch any of the stretch net when adding the elastic (especially the leg elastic).
Yay you're all finished, you can now admire your gorgeous tutu ultimate swimsuit.
Happy sewing
Xx Katy
